Electromagnetic clutch and method of closing and opening an electromagnetic clutch

Abstract

An electromagnetic clutch is provided, which includes a shifting sleeve having a first toothing arranged in a rotationally fixed manner on a first shaft and can be displaced linearly along the first shaft between an engaged and a disengaged state, a first clutch body, which has a second toothing and which is aligned coaxially to the first shaft, the first and/or the second toothing having undercuts in the direction of the engaged state, which are configured such that a torque transmission between the first shaft and the first clutch body generates a force on the shifting sleeve in the direction of the engaged state. Also included is a method of closing and opening an electromagnetic clutch.

The invention claimed is: 
     
         1 . An electromagnetic clutch, comprising:
 a shifting sleeve which has a first toothing, is arranged in a rotationally fixed manner on a first shaft and can be displaced linearly along the first shaft between an engaged and a disengaged state,   a first clutch body, which has a second toothing and which is aligned coaxially to the first shaft,   a stator, which includes a first coil, which serves for the direct or indirect displacement of the shifting sleeve linearly along the first shaft,   wherein the first and/or the second toothing has/have undercuts in the direction of the engaged state, which are configured such that a torque transmission between the first shaft and the first clutch body generates a force on the shifting sleeve in the direction of the engaged state, and   wherein, in the engaged state, there is a positive fit due to the first and the second toothing between the shifting sleeve and the first clutch body,   wherein an armature is provided which is coupled to the shifting sleeve, and wherein the armature is adapted to be displaced along the first shaft by energizing the first coil, the armature and the shifting sleeve being coupled so as to be displaceable relative to each other in the axial direction, and   wherein a displacement of the armature by the first coil is limited by a stop which is provided on the first clutch body, and wherein, when the armature rests against the stop when the first coil is energized, there is a magnetic holding force which acts on the armature.   
     
     
         2 . The electromagnetic clutch according to  claim 1 , wherein the first coil serves for direct or indirect displacement of the shifting sleeve linearly along the first shaft into the engaged state, and wherein the stator comprises a second coil, which serves for direct or indirect displacement of the shifting sleeve linearly along the first shaft in the direction opposite to the engaged state and/or wherein a spring return is provided which applies a spring force to the shifting sleeve linearly along the first shaft in the direction opposite to the engaged state. 
     
     
         3 . The electromagnetic clutch according to  claim 1 , wherein the first coil serves for direct or indirect displacement of the shifting sleeve linearly along the first shaft into the engaged state, and wherein a spring return is provided which applies a spring force to the shifting sleeve linearly along the first shaft in the direction opposite to the engaged state. 
     
     
         4 . The electromagnetic clutch according to  claim 1 , wherein when the shifting sleeve is displaced by the first coil into the engaged state, there is an axial overlap between the first and the second toothing and the undercuts move the shifting sleeve towards the engaged state when torque is transmitted. 
     
     
         5 . The electromagnetic clutch according to  claim 1 , wherein the first and/or the second toothing provided with undercuts has/have teeth, wherein tooth flanks of the teeth are wedge-shaped at least along a section of the tooth in a plan view. 
     
     
         6 . The electromagnetic clutch according to  claim 5 , wherein the first and the second toothing have undercuts and tapered ends of the wedge-shaped sections of the first and the second toothing extend in opposite directions. 
     
     
         7 . The electromagnetic clutch according to  claim 1 , wherein the armature and the shifting sleeve are coupled via at least a first spring unit which is elastic in the axial direction and which deflects when the shifting sleeve and the armature are displaced axially relative to each other. 
     
     
         8 . The electromagnetic clutch according to  claim 7 , wherein the armature has a first axial abutment surface and the shifting sleeve has a second axial abutment surface, and wherein the first spring unit is supported in the axial direction on the first and the second axial abutment surfaces. 
     
     
         9 . The electromagnetic clutch according to  claim 8 , wherein the armature has a radial web on which the first axial abutment surface is provided. 
     
     
         10 . The electromagnetic clutch according to  claim 9 , wherein the first spring unit is present on an axial side of the web and a second spring unit is present on the opposite side of the web, at least one of the spring units exerting a restoring force when the armature and the shifting sleeve are displaced relative to each other. 
     
     
         11 . The electromagnetic clutch according to  claim 10 , wherein the spring units are accommodated in spaces which are delimited radially on the inside by a shifting sleeve bushing and radially on the outside by the armature and on one end face by the web and on the opposite end face by a toothed wheel firmly connected to the shifting sleeve bushing, wherein the toothed wheel has the first toothing and engages in the second toothing provided on the first clutch body in the engaged state. 
     
     
         12 . The electromagnetic clutch according to  claim 7 , wherein the at least one spring unit comprises at least one wave ring or a diaphragm spring or an assembly with at least one wave ring and a diaphragm spring. 
     
     
         13 . The electromagnetic clutch according to  claim 7 , wherein at least one spring unit is arranged such that, when the shifting sleeve is coupled to the first clutch body, this spring unit is preloaded to exert a spring force on the shifting sleeve in the direction of the disengaged state. 
     
     
         14 . The electromagnetic clutch according to  claim 1 , wherein at least one spring unit is arranged such that when the first and the second toothing are in contact on an end face and the shifting sleeve is not yet coupled to the first clutch body, the spring unit pretensions the shifting sleeve in the direction of the engaged state. 
     
     
         15 . The electromagnetic clutch according to  claim 1 , wherein a second clutch body is provided, which is aligned coaxially to the first shaft and is provided on the axial side of the shifting sleeve opposite to the first clutch body and can be coupled to the shifting sleeve by actuating a second coil, which serves for direct or indirect displacement of the shifting sleeve linearly along the first shaft in the direction opposite to the engaged state, wherein a toothing of the second clutch body and a toothing of the shifting sleeve associated with the toothing of the second clutch body are formed like the toothing of the first clutch body and the toothing associated with the toothing of the first clutch body. 
     
     
         16 . The electromagnetic clutch according to  claim 15 , wherein, when the shifting sleeve is moved into the engaged state along with the second clutch body, a spring unit acts on the shifting sleeve before and after the engagement in the direction of the engaged state or the disengaged state. 
     
     
         17 . An electromagnetic clutch, comprising:
 a shifting sleeve which has a first toothing, is arranged in a rotationally fixed manner on a first shaft and can be displaced linearly along the first shaft between an engaged and a disengaged state,   a first clutch body, which has a second toothing and which is aligned coaxially to the first shaft,   a stator, which includes a first coil, which serves for the direct or indirect displacement of the shifting sleeve linearly along the first shaft,   wherein the first and/or the second toothing has/have undercuts in the direction of the engaged state, which are configured such that a torque transmission between the first shaft and the first clutch body generates a force on the shifting sleeve in the direction of the engaged state, and   wherein, in the engaged state, there is a positive fit due to the first and the second toothing between the shifting sleeve and the first clutch body,   wherein an armature is provided which is coupled to the shifting sleeve, and wherein the armature is adapted to be displaced along the first shaft by energizing the first coil, the armature and the shifting sleeve being coupled so as to be displaceable relative to each other in the axial direction,   wherein the armature and the shifting sleeve are coupled via at least a first spring unit which is elastic in the axial direction and which deflects when the shifting sleeve and the armature are displaced axially relative to each other, and   wherein at least one spring unit is arranged such that, when the shifting sleeve is not yet coupled to the first clutch body, this spring unit is preloaded to exert a spring force on the shifting sleeve in the direction of the engaged state.   
     
     
         18 . A method of closing and opening an electromagnetic clutch, including an armature and a shifting sleeve coupled thereto, which has a first toothing, is arranged in a rotationally fixed manner on a first shaft and can be displaced linearly along the first shaft between an engaged and a disengaged state, a first clutch body having a second toothing, which is aligned coaxially to the first shaft, a first coil, which serves to displace the shifting sleeve linearly along the first shaft into the engaged state, and a second coil, which serves to displace the shifting sleeve linearly along the first shaft against the engaged state, the method comprising:
 a) applying voltage to the first coil and generating a magnetic force acting on the armature towards the first clutch body;   b) displacing the armature and entraining the shifting sleeve by the armature from a disengaged state in the direction of the engaged state with the interposition of a spring unit between the armature and the shifting sleeve;   c) moving the shifting sleeve into the engaged state of the shifting sleeve and forming a positive fit between the shifting sleeve and the first clutch body by the first and the second toothing, the first and the second toothing having a first axial overlap with respect to each other;   d) transmitting a torque between the first clutch body and the first shaft and displacing the shifting sleeve relative to the armature towards the first clutch body, the first and the second toothing having a second axial overlap with respect to each other, which exceeds the amount of the first one;   e) canceling or reducing the transmitted torque between the first clutch body and the first shaft and displacing the shifting sleeve relative to the armature away from the first clutch body, the first and the second toothing having the first axial overlap with respect to each other;   f) canceling or reducing the magnetic force acting on the armature by the first coil;   g) applying voltage to the second coil and generating a magnetic force acting on the armature; and   h) displacing the armature and entraining the shifting sleeve by means of the armature from an engaged state to the disengaged state.